The present invention is in the field of inductive devices and relates more particularly to a chip type inductive device characterized in its being surface mountable, of small size and low profile, high power handling capacity and, most especially, readily adapted to be designed to extremely tight tolerances.
Devices of this sort are employed in connection with cellular phones, personal communication networks, cable TV, global positioning systems, vehicle location systems, all types of high frequency filters and all similar high frequency equipment, to frequencies of 2400 MHz.
Prior Art
Conventional miniaturized inductors have heretofore been of two general types, namely wire wrapped chips and monolithic ferrite chips. The wire wrapped chips exhibit poor mechanical properties, are generally far larger than desirable, and are poorly designed for use in surface mounting applications. More particularly, in current circuit applications it is highly desirable for a component to be of low profile, and the wire wound chips are, in all instances, high profile devices.
A second type of inductor is formed of a monolith of ferrite. Chips of this sort exhibit poor high frequency performance.
It has been proposed in various prior art references to provide a miniature inductor suitable for high tolerance applications. By way of example, reference is made to U.S. Pat. No. 4,310,821, which discloses a printed inductance device formed on a foldable substrate.
U.S. Pat. No. 4,313,152 is directed to a miniaturized electrical coil comprised of a plurality of spiral coils with multiple connectors between the coils, the coils being configured to minimize capacitance.
U.S. Pat. No. 4,543,553 relates to a chip type inductor comprised of a multiplicity of magnetic layers, each layer having only a portion of an inductive pattern, the layers being interconnected to form a continuous coil. Terminations may be formed on the end faces to render the chip suitable for surface mounting.
U.S. Pat. No. 4,613,843 discloses a transducer for an automobile and including a coil on a ceramic substrate which is located adjacent a moving magnet for use in sensing various crankshaft positions. The coil of this device is comprised of one or more superposed flat layers which are spirally wound and which are formed by metal deposition techniques.
U.S. Pat. No. 4,626,816 discloses a flat coil assembly comprised of a series of spiral conductive coils on a insulative slab having jumpers connecting the inner ends of the coils, the outer ends of the coils being connected to pads on the slab.
U.S. Pat. No. 4,641,114 is directed to a delay line comprised of a multiplicity of circuits stacked one atop the other. Each delay circuit is formed of a solid sheet of conductive material etched to a spiral configuration, the ends of successive layers being connectable in series via separate contact pads.
U.S. Pat. No. 4,803,543 is directed to a laminated transformer comprised of a plurality of ferrite sheets on which conductive patterns are formed and which are sintered to define the transformer. Each layer includes a partial coil which is connected to the adjacent layer to define a completed circuit.
U.S. Pat. No. 4,926,292 is directed to a thin film printed circuit inductive device comprised of a conductive spiral having resistive links connected between adjacent turns to minimize inherent resonances.